Part 1: Direct Transmission Human to Human

Transcription

1 Buzz Buzz Bite! Part 1: Direct Transmission Human to Human Direct human- to- human disease transmission occurs between an infected person and an uninfected person. Examples of diseases spread through direct transmission between humans include the common cold (rhinovirus), flu (influenza) and AIDS (acquired immune deficiency syndrome). Direct transmission can result from direct contact (touching, bodily fluids) or indirect contact (touching an infected surface). Instructions: Each cup of liquid represents the bodily fluids of a human. Someone in the class will receive fluids infected with a disease. You do not know who is infected and who is not, but this investigation will allow you to figure out who introduced the disease into the population. That person is the index patient, sometimes called Patient Zero. Materials (for each student): One disposable cup with unknown liquid One disposable plastic pipet Hints: Only exchange once per round. Do not exchange with the same person twice. Both partners exchange during each round. Procedure (This game will remind you of Musical Chairs!): Caution: Some of the liquids are poisonous to taste or touch. Do not drink any fluids in this lab. If a liquid spills on your skin, wash it off immediately with plenty of cold water. Choose a cup and pipet. Record the cup number in the Data Table. Students with odd- numbered cups form a circle. Students with even- numbered cups walk around the outside of the circle. Round 1: When instructed, students in the outer circle will begin to walk around the inner circle. When the teacher gives the signal, stand in front of someone sitting in the inner circle. When instructed, squirt two pipets full of fluid from your cup into the cup of the person in front of you. Your partner will do the same. Record your partner s cup number in the Data Table. Then wait for everyone else to finish. Round 2: When instructed, the outer circle will walk around the inner circle again and each student will find a new partner. Repeat the fluid exchanges just as in Round 1. Do not exchange with the same person twice. Record your new partner s cup number. Wait for everyone to finish. Round 3: Repeat this procedure one more time and then return to your seat. Your teacher will add an indicator solution to each cup. Infected students will see a color change.

2 Conclusion: Make a chart to track disease transmission. Can you figure out who was originally infected? DATA TABLE: Your Did any errors occur in this lab? If so, how do you think these errors will affect the results? Round 1 Round 2 Round 3 Who was originally infected? DATA CHART Round Round 2 Round 3 Results (+/ )

3 Buzz Buzz Bite! Part 2: Indirect Transmission Human to Vector to Human The second part of this activity simulates indirect vector- borne disease transmission. Transmission is indirect when humans transmit the disease to other humans, but not directly person- to- person. A vector, such as a mosquito, picks up the pathogen (disease- causing organism) from an infected human and passes it to an uninfected human. One person transmits the disease to another person, even though there is no direct contact. Examples of vector- borne diseases include chikungunya, dengue fever, and malaria. Instructions: Students are either Humans or Mosquitoes. Divide the class in half randomly by cup selection. Each cup of liquid represents the bodily fluids of either a human or a mosquito. Someone in the class will receive fluids infected with a disease. You do not know who is infected and who is not. Note: Only Humans will be initially infected in this activity, in order to demonstrate how infected humans can transmit pathogens indirectly to uninfected humans through a mosquito vector. Materials: Hints: Only exchange once per round. One disposable cup with unknown liquid Do not exchange with the same person twice. One disposable plastic pipet Only Mosquitoes have pipets to exchange. (for Mosquitoes only!) (Humans cannot bite Mosquitoes!) Procedure (Same as Part 1, this game will remind you of Musical Chairs): Caution: Some of the liquids are poisonous to taste or touch. Do not drink any fluids in this lab. If a liquid spills on your skin, wash it off immediately with plenty of cold water. Everyone chooses a cup, but only Mosquitoes take a pipet. Record your cup number in the Data Table. Humans form a circle. Mosquitoes walk around the outside of the circle. Round 1: When instructed, students in the outer circle will begin to walk around the inner circle. When the teacher gives the signal, stand in front of someone sitting in the inner circle. When instructed, Mosquitoes squirt two pipets full of fluid from your cup into the cup of the Human in front of you. (A mosquito can transmit virus in its saliva when it bites a human.) Mosquitoes then take two pipets full of fluid from the Human s cup. (When taking a bloodmeal, a mosquito can consume virus in the human s blood.) Record your partner s cup number in the Data Table. Then wait for everyone else to finish.

4 Round 2: When instructed, the outer circle will walk around the inner circle again and each student will find a new partner. Repeat the fluid exchanges just as you did in Round 1. Do not exchange with the same person twice. Record your new partner s cup number. Wait for everyone to finish. Round 3: Repeat this procedure one more time and then return to your seat. Your teacher will add an indicator solution to each cup. Infected students will see a color change.

5 Conclusion: Make a chart to track disease transmission. Can you figure out who was originally infected? DATA TABLE: Your Did any errors occur in this lab? If so, how do you think these errors will affect the results? Round 1 Round 2 Round 3 Who was originally infected? RESULTS CHART Round 1 Mosquito 1 Mosquito 2 Mosquito 3 Mosquito 4 Mosquito 5 Mosquito 6 Mosquito 7 Mosquito 8 Mosquito 9 Mosquito 10 Mosquito 11 Mosquito 12 Human 1 Human 2 Human 3 Human 4 Human 5 Human 6 Human 7 Human 8 Human 9 Human 10 Human 11 Human 12 Round 2 Round 3 Results (+/ )

6 Buzz Buzz Bite Teacher Notes Part I is a classic direct disease transmission lab often used to demonstrate HIV or influenza transmission from person- to- person contact. Part II is an adaptation of this lab to simulate indirect transmission of vector- borne diseases. This section demonstrates transmission of the chikungunya virus (ChikV) by Aedes sp. mosquitoes, causing the disease chikungunya in humans. Reagents: Measurements do not need to be exact. Infected Solution: Indicator Solution: Sodium carbonate (washing soda) 1 g = approx. ¼ teaspoon 100 ml water Phenolphthalein: 0.1 g = approx. ¼ of 1/8 teaspoon 100 ml ethyl or 70% isopropyl (rubbing) alcohol Phenolphthalein indicator will turn dark pink or red in the presence of a base (washing soda). Non- toxic Reagents: Measurements do not need to be exact. Infected Solution: Indicator Solution: 2 tbsp. baking soda 500 ml of water 1/4 tsp. turmeric 4 tbsp. isopropyl (rubbing) alcohol Game Play: Turmeric indicator solution will turn orange or red in the presence of a base (baking soda). Depending on the number of students in your class and grade level, students can play both parts of the game in approximately one 50- minute class period. This timeframe does not include a discussion of direct vs. indirect transmission and the chikungunya virus, which is necessary to understand the lesson. Direct vs. indirect transmission is discussed in the Introduction to the lab activities. Articles and video clips about chikungunya are on the website. If you have a large number of students, it might be more time efficient to split the class. Half of the students play Part I while the other half observe and record data; then they switch roles for Part II. Everyone gets to play one version of the game, but there is less movement in the classroom and less data to analyze. Some teachers assign the data analysis for homework to save class time.

7 Procedures: Part I (Direct Transmission): This activity requires an even number of students. Number the cups sequentially: 1, 2, 3, etc. Each student takes a cup of fluid and a pipet. Approximately 10% of the class should receive infected solution and the rest of the cups should contain water. Fill all cups with the same volume of fluid and record the cup numbers of those infected. Be careful to avoid cross- contamination. The following suggestions may help you keep track of exchanges: o Project a blank chart from the handout onto your smart board or screen using a document camera. o Post a chart or paper on the board for the students or teacher to fill in data after each exchange. o Attach a sticky note to each cup to record exchanges. Use logic to determine the transmission pathway and identity of the initial infected patient. Part II (Indirect Transmission): This activity requires an even number of students. Half are Mosquitoes and half are Humans. Assign roles to students or allow them to select for themselves. Number the cups sequentially: M1, M2, M3, etc. for Mosquitoes; and H1, H2, etc. for Humans. Each student takes a cup of fluid, but only Mosquitoes take a pipet because Humans cannot bite Mosquitoes. All Mosquitoes are females that must feed on blood to develop their eggs. The pipet represents the Mosquito proboscis (mouthpart) to bite and take a blood meal. Only Humans will be initially infected in this activity, in order to demonstrate how infected humans can transmit pathogens indirectly to uninfected humans through a mosquito vector. Approximately 10% of the Humans should receive infected solution and the rest of the cups should contain water. Fill all cups with the same volume of fluid and record the cup numbers of those infected. Be careful to avoid cross- contamination. The following suggestions may help you keep track of the exchanges: o Project a blank chart from the handout onto your smart board or screen using a document camera. o Post a chart or paper on the board for the students or teacher to fill in data after each exchange. o Attach a sticky note to each cup to record exchanges. Use logic to determine the transmission pathway and identity of the initial infected patient.